In the manufacture of paper from waste paper, the introduction of waste paper results in the presence of tacky impurities called stickies. The term "stickies" covers, among others, resin, dispersions for higher-value end products, hot melts for backings and also print ink binding agents as the most important material groups. Stickies, in other words adhesive impurities, represent a significant stumbling block in waste paper processing and especially affect the runnability of the paper machine and the quality of the end product. Stickies are essentially divided into micro- and macrostickies, with the dividing line arbitrarily set at 150 microns, since only above this size is it possible to mechanically separate out the sticks. The reduction in size of the slot widths of the sorting baskets down to 150 microns, which has been pursued over the past years, resulted in a significantly improved separation of macrostickies. Total elimination of macrostickies has not been achieved, however, despite these technologies. This proves that microstickies, present in the cycles, agglomerate into larger units, in other words macrostickies, after the macrostickies have been separated out, due to the constant fluctuations of pressure, temperature and ph as well as mechanical effects. According to the current state of the art in sorting, the elimination of microstickies in waste paper processing has the greatest potential in the fight against stickies.
In order to overcome the microstickie problem, the following techniques were suggested:
Fixing the anionic part of the microstickies to the paper fiber by means of a highly cationic, synthetic liquid substance (Poly-DADMAC, PAC, polyamine, etc.) and removal from the paper machine cycle. This technique barely reduces deposits in the dry section of the paper machine or the deposits on the calender rolls. There is also a potential negative interaction with other paper auxiliaries (coacervation). The problem itself is recycled with the next waste paper cycle, since the stickies remain in the end product.
Adsorption without removal: Dosing of minerals in the area of the paper machine. This is intended to sheathe or "de-stick", in short inhibit, macrostickies in the paper machine cycle. However, it increases the amount of fillers in the end product which, in turn, adversely affect the strength properties and optical properties of the manufactured paper. Here, too, the problem is recycled with the next waste paper cycle, since the inhibited stickies remain in the end product.
Addition of polymers with one hydrophobic and one cationic end each: These products are added in liquid form tot he primary cycle of the paper machine itself. In practice, this has had no effect on the dry section or the calender rolls, i.e. the deposits in the dry section or on the calender rolls hardly diminished. Here, too, the problem is recycled with the next waste paper cycle, since the stickies remain in the end product.
All these recommendations merely gloss over the real problem of the presence of stickies. This also shows that there is a need for action for solving the problems caused by stickies, especially microstickies, remaining in the paper pulp.
The goal of the invention is to create a method, based on the described state of the art, to eliminate the problems caused by stickies, especially microstickies.